The present invention relates to electromagnetic transducers such as may be employed in disk or tape storage systems.
Electromagnetic transducers such as heads for disk or tape drives commonly include Permalloy (approximately Ni80Fe20), which is formed in thin layers to create magnetic features. For example, an inductive head may have conductive coils that induce a magnetic flux in an adjacent Permalloy core, that flux employed to magnetize a portion or bit of an adjacent media. That same inductive head may read signals from the media by bringing the core near the magnetized media portion so that the flux from the media portion induces a flux in the core, the changing flux in the core inducing an electric current in the coils. Alternatively, instead of inductively sensing media fields, magnetoresistive (MR) sensors or merged heads that include MR sensors may have thin layers of materials that are used to read magnetic signals by sensing changes in electrical resistance of the MR sensor that are caused by such signals.
In order to store more information in smaller spaces, transducer elements have decreased in size for many years. One difficulty with this deceased size is that the amount of flux that needs to be transmitted may saturate elements such as magnetic pole layers, which becomes particularly troublesome when ends of the pole layers closest to the media, commonly termed poletips, are saturated. Magnetic saturation in this case limits the amount of flux that is transmitted through the poletips, limiting writing or reading of signals. Moreover, such saturation may blur that writing or reading, as the flux may be evenly dispersed over an entire poletip instead of being focused in a corner that has relatively high flux density. For these reasons the use of high magnetic moment (high Bs) materials in magnetic core elements has been known for many years to be desirable. For instance, iron is known to have a higher magnetic moment than nickel, so increasing the proportion of iron compared to nickel generally yields a higher moment alloy. While a number of other high-magnetic moment materials are known in the art, such as Sendust (Fexe2x80x94Nixe2x80x94Al) and CoZrTa, the use of predominantly-iron NiFe alloys, such as Ni45Fe55, has advantages including similarities to Permalloy that can facilitate forming high moment elements.
As noted in U.S. Pat. No. 5,606,478 to Chen et al., the use of high moment materials has been proposed for layers of magnetic cores located closest to a gap region separating the cores. Also noted by Chen et al. are some of the difficulties presented by these high moment materials, including challenges in forming desired elements and corrosion of the elements once formed. Chen et al. note that magnetostriction is another problem with Ni45Fe55, and teach the importance of constructing of heads having Permalloy material layers that counteract the effects of that magnetostriction. This balancing of positive and negative magnetostriction with plural NiFe alloys is also described in U.S. Pat. No. 5,874,010 to Tao et al. Anderson et al., in U.S. Pat. No. 4,589,042, also suggest that magnetostriction may be a problem with Ni45Fe55, and teach the use of high moment Ni45Fe55 for poletip layers.
Another difficulty encountered with thin film inductive heads involves the shape of the pole layers near the poletips. The pole layers typically curve outward from the poletips in order to circumvent the coil and insulation layers sandwiched between the pole layers. This curvature between layers that are parallel in the vicinity of the recording gap can allow bleeding of the signal across the curving pole layers, diminishing fringing fields from the gap that are used to write on the media. Also problematic can be accurately defining the poletips, which may each be formed as part of a pole layer through a much thicker mask layer. An indefinite poletip width causes the track width of the head to be uncertain. To overcome these problems, U.S. Pat. No. 5,285,340 to Ju et al. and U.S. Pat. No. 5,452,164 to Cole et al. teach forming poletips in separate steps from forming pole layers, and stitching the poletips to the pole layers so that magnetic continuity is established between the intimately connected pole layers and poletips.
The combination of MR sensors with inductive heads introduces additional complications. Although the MR sensor may be unshielded, a pair of magnetically permeable shields usually sandwiches the sensor in order to restrict the magnetic fields reaching the sensor, essentially focusing the sensor. In one type of combined head, sometimes termed a piggyback head, the shields are separated from the inductive transducer by a layer of nonmagnetic material such as alumina (Al2O3). An integrated head, on the other hand, uses the pole layers of the inductive transducer as shields for the MR sensor, which is formed in the recording gap in order to ensure that the sensor and inductive transducer are aligned with the same recording track of the medium despite any skewing of the head relative to such a track. Perhaps the most common type of head currently employed for hard disk drives is a merged head, in which one pole layer of the inductive transducer forms one shield of the sensor.
U.S. Pat. No. 5,850,325 to Miyauchi et al. teaches reducing the separation between the shield and pole layers of a piggyback head to a layer of nonmagnetic material that is thin enough to allow coupling between the shield and pole layers. With the exception of a recording gap, such an inductive transducer ensures a continuous magnetic circuit through the pole layers, since it is known that any feature that increases the reluctance associated with magnetic portions of the head decreases the efficiency of that head. Further discussion of the requirements and challenges of transducer technology can be found in Magnetic Recording Technology, 2nd Edition, C. Denis Mee and Eric D. Daniel, Chapter 6, incorporated herein by reference.
The present invention provides a magnetic head that overcomes the challenges outlined above to provide superior performance. A magnetically isolated poletip is located between a shield of an MR sensor and a write pole of an inductive sensor. The poletip is preferably made of high Bs material, allowing the flux that travels through the much larger pole layer to funnel through the poletip without saturation. The poletip is isolated from the shield layer in order to decouple the shield layer from Barkhausen noise that may occur in the poletip, which in turn reduces noise in the sensor, while the shield layer serves to complete the inductive circuit. Despite having a poletip surrounded by nonmagnetic material, heads built according to this invention have demonstrated high overwrite as well as remarkably low noise.